Thank ,
Google has published the assistant sdk,it is very interesting :
https://developers.google.com/assistant/sdk/
But meanwhile a b4a library for assistant sdk is ready I am trying to use ifttt service to connect my app to google home mini.
With ifttt I can get a firebase push notification through they webhook service , but I didn't know what write into the field.
To send the push message, the webhook needs an url and a body message, the URL I think is
https://fcm.googleapis.com/fcm/send
But I can understand what write into body field.